Multiplex signaling



Nov. 19, 1935. A. M. NICQLSON 2,021,743

MULTIPLEX S IGNALING Filed June 13, 1930 5 Sheets-Sheet 1 Q I w mm (1 mm m m .10. vpnu wof) 993,

ATTORNEY Nov. 19, 1935. A. MCL. NICOLSON 2,

MULTIPLEX SIGNALING Filed June 15, 1930 5 Sheets-Sheet 2 F1 22-- I 519na/ Channels 5 C IZ545678SIQIIIZISHISIGIIISIQZO 77r'ne Units INVENTOR Alexander M Lean Nico/s on,

BY JM/KMW ATTORNEY Nov. 19, 1935-. A, MCL, NICOLSON 2,021,743

' MULTIPLEX SIGNALING Filed June 15, 1930 5 Sheets-Sheet 5 TEE- 4k I NVENTOR Alexander- M Lean lV/io/jon BY @M/FWW ATTORN EY Patented Nov. 19, 1935 2,021,143 murmrmx smmnnm Alexander mum Nicolson, New York, N. 1., I assignor to Communication Patents, Inc., New York, N. Y., a corporation of Delaware Application June 13,1980, Serial No. 460,806

i 9 Claims. (Cl. 179-15) UNITED 1 STATES This invention relates to multiplex transmission in general, and "particularly to the transmission of a plurality of dependent or independent signals over a single channel of wire conductors or of a carrierfrequency.

An object of ,this invention is to transmit an .extremely large number of electrical signals over a singlecommunication channel.

Another object of this invention is to obtain an electrical commutator having no mechanically moving parts. /W

A further object of the invention is to obtain perfect synchronization between electrical com mutators separated from one another.

Heretofore, it has been possible to transmit several conversations over a single pair of conduc-.

tors. Within a certain carrier frequency range having definite limits, a number of broadcasts or independent programs-have been transmitted. Within another frequency range telegraph circuitshave been operated to transmit a number of telegraph messages. In substantially all of the above. mentioned systems, separation of one signal from the other has been effected through the use of different transmitting or carrier frequencies. For instance, one conversation or signaling channel will have a carrier frequency of 50,000 cyclesusing a band width, if the signal is I sound and both side bandsare transmitted, of

, 12,000 cycles lying between 44,000 and 56,000

cycles.- The next carrier frequency channel for sound will necessarily be spaced at least 6,000

cycles from 50,000 cycles'to prevent interference between signals. Practically, however, this frequency spacing must be much greater. It is obvious, therefore, that with the carrier frequencies available, the number of signaling channels withj in the usable range is essentially limited.

' of one signal and the negative half cycle for the 1 It is also known that two-way conversations or two independent transmission channels may be accomplished on the same carrier frequency by using the positive half cycle for the transmission transmission of the other signal. Adoption of this method, however, will only double the number of usable channels.

The present invention contemplates obtaining a substantially unlimited number 01 signaling metropolitan area such asNew York, that is, it is possible to combine 10 or. 15 of. the present ex- Furthermore, this channels upon either a single carrier frequency or over a single pair ot conductors. For telephone use, one centralstation can serve a large changes into one exchange. I invention permits all broadcasting stations to use curve.

signal into The invention is based upon time division,'time I being the sole basis upon which signals are separated from one another instead of upon the basis of frequency separation in which time is only partially involved. It is well known that any signal having energy of a vibratory nature, may be 10 transformed into electrical currents having definite frequencies, the combination of which will form a certain wave shape. Viewing the signal,

therefore, from the standpoint of wave shape in the form of a curve, such a-signaling curve may 1 be reproduced by the transmission of a certain number of the component parts thereof; In other words, a voice conversation or single words or letters may be transmitted intelligently by the trans- I mission of only a portion of each word or letter or even a portion of the conversation.- The transmission, therefore, of a suflicient number of points upon'any curve will reproduce the For instance, a curve of any configuration extending over a length of one inch is divided into 10,000 parts on, a horizontal basis.v By eliminating 99 parts out of each 100, it is conceivable that the curve can be' reproduced sufllciently. complete for all practical purposes. If this inch curve be further divided into 1,000,000 points, and every ten thousandth p'oint be reproduced, the same number of points at the same position will occur, reproducing the same curve as when the inch distance was divided into only 10,000 divisions. In the case when the curve was divided into 1,000,000 divisions, however, there is provided space for 9,999 other wave shapes, which can be interpositioned between the 100 points representing the-flrst-curve. By repeating the 10,000 division plan 100 times 40 within the inch, the same result is obtained.

From the above brief explanation, which outlines the principle upon which applicants invention is based, it may be seen thatby dividing a sumciently small increments, it is unnecessary to transmit a large number thereof to make the signal perfectly intelligible when the increments are reproduced thereby providing time to transmit increments oi other signals. signal which ispossibleof transformation into electrical vibrations'may be transmitted in this mannerv such as television signals, voice signals, telegraph signals, etc.

A feature of thisinvention is the use of a thermionic commutator. This commutator hosts I 2 o no mechanical partswhatever and is capable of rotating at a'espeed correspondingvto the speed of transmission of electric current or of the speed 01' light which is exceedingly faster than any mechanical system may be forced to rotate.

With such a commutator, timecan be divided tion, the continuity of the signals being ma.in-

tained by the large number-of signal portions am, as parallel connections will serve as well. The transmitting apparatus may be a high frequency carrier wave or may be simply amplifiers of any type. the operation of which is the same as in electrical transmission systems well known 5 in them.

' In Fig. 2 the signal sources or -channels A't o channel circuits and adds the impulses for recepwithin definite limits. Between; the impulses 1 of any one signal, however, many other channels tive receivers. l I

The details of the invention will be more thor-- oughly understood by reference to the accompanying drawings. in which: I

Figures 1a andlb are diagrammatic drawings of a transmission system and a receiving system,

respectively;

- Fig. 2 is a signal time chart showing the method-of segregating the signal channels into time units; 1

Fig.3 is a time curve chart showing how three curves representing waveforms may be transmitted-by reproduction oi a sufl'lcient number of points thereon; o

Fig. 4' is a schematic diagram of ageneratortranslator circuit as an individual unit:

Fig. 5 isa curve diagram of the currents in the system of Fig. 4; e I

Fig. 6 is a schematic drawing of a modification of the system of Fig. 4;

Fig.7 is a circuit arrangement of generator and translator;

Fig; 8 is a circuit arrangement of a modificaa combined tionof the system of Fig. 7 showing a synchronizing circuit used withtwo'thermionlc commutators;

r Fig. 9 is a current a 8; and e a Fig; 1.0 is a partial schematic drawing of a the systems of Figs. 7 and 8.

Referringto Fig. la particularly, signal sources I which maybe of any type of electrical vibrations constituting particular forms of intelli-,.

gence, are represented at A to J, inclusive. These channels are shown connected to a transmitting commutator 4, in-whioh they are divided intotimeunits. The output circuits of the commutatorfare combined and impressed upon trans- "mission apparatus 5, the. output circuit of which is connected with a space wire conductors I;

' InFig. lb a receiving antenna l and wire con- ..paratus [0 which impresses its output on a re-- may be transmitted and received at their respec chart of the system of F18.

coupling between tubes which may be used in" antenna system 8 or ductors 9 are shown connected to receiving ap- I 1 eiving commutator ll similar to that of the.

. points. 2, I2, 22, 32

J ofFlgs. la. and 1b, respectively, are shown along thevertical axis extending horizontally, and their sesregations shown along the horizontal 10 axis.- Channel A for instance will take thefirst time unit; signal B the second time unit; .signal F the third time unit; and so on as shown in the diagram. These signal sources are handled by a thermioniccommutator having an equal num- 15 her of-time channels, two revolutions of which are shown on the chart. This may be modified, of course, by using acommutator having a larger capacity of time channels, only ten of which are employed for the transmission of these ten 20 sources. In that case there would be a space on the chart between the tenth and eleventh unit, which is nine times as large as ten units now shown assuming that the commutator has the these curves representing positive halfv cycles of 35 three wave forms such as speech 'ior instance, which may be the signal sources A," B, and F of the preceding figures. The time units corresponding with the chart oi. Fig. 2 are shown by thepoints |,2,s;||, I2, 13 21,-2'2, 23, etc. This 40 diagram illustrates, therefora'that the points I, ll, IIJI, 4| n produce the curve A, while M n+1,produce the curve B,.and points'i il, 23,33 n+2 produce the curve ,F. The signal transmissions have been 45 shown as points on the curve,but in fact are appreciable 'lengthsj thereof. Furthermore, for clearness, only a few, points have been taken to represent the operation of the system, but it is apparent that by greatly subdividing these sig- 50 nals permitting the transmission of many intermediate portions, a more perfect reproduction is obtainable.

Toaccomplish this rapid signal dividing, the system shown in Fig. 4 may be used. This system comprises two units, oneof which is a threephase generator source comprising a vacuum tube 15 and quadrature field unit it having a delta output transformer l8. The other unit is the translator comprising three vacuum tubes 20, 2i, and 22, the inputs to which are transformers 24, 26, and 26, and the outputs of which are transformers 21, 2B and. Referring to-the generator in detail, it is of the type disclosed in R.' D. Duncan,Jr., Patent No. 1,578,881, dated March 30, 1926; .theoscillator comprising a tube It,

having arsed-back condenser 30 and tuningcleerated. Inthe present gene'ratorthree phase currents are being induced in windings lll, ll, and 42 disposed 120? apart and connected to the primary winding of delta transformer it. These three phase currents govern or control the transmission-through vacuum tubes 2|, 2i, and 22, that is, vacuum tube 20 of the translator will be made operative during "the positive half cycleof one phase of the control current, while yacu- 22 will be operative during 0nd. When the tube .placing intermittently thereon, a

. translator of Fig. 4 has um tube M will be operative during the positive half 'cycle of the second phase, and vacuum tube the positive half cycle The three signals, therefore, A, B, and F shown in Fig. 3 arriving in the input transformers 24, .25, and 25, respectively, are each. transmitted during one-third of the frequency time of the generated frequency.-

For instance, if the frequency is 900 cycles per second, then 900 impulses of each signal aresent duringeach second but each time-unit will be 1/2700 of a second in length. That is, each signal will occupy of a second divided into 900 time units of Referring to Fig. 5, the three phase control frequency impulses are shown as a, b, and c. The shaded 1 portions of these curves represent the portion of the three phase currents which are effective in controlling or operating the tubes, since the grids of thetubes are biased sufficiently to prevent any plate current flowing until the positive impulse has reacheda value shown by of the third phase.

the horizontal line at the intersections of the 1/2700 of a second and immediately upon cessation of operation, phase I) will place the tube 2| in an operating condition'for ilz'lofl of'a sec- 2i is made inoperative by the removal of the positive potential, tube 22 immediately becomes operative by virtue of the positive potential placed on its grid by phase 0.

is made operative by positive bias such as to operate the tube durin fideflnite period.

Referring to Fig.

In other words, each tube 6, this modification of the five time channels. The

coils' 50, ii, 52, 53, and 54 have induced therein five phase currents by placing them in the quad- .of the tubes are eration thereof during the portion of the positive rature magnetic field of the generator in Fig. 4.

These flve'phase currents are impressed upon vacuum tubes 56, 51, 58, 59, and 60, respectively, through the pentagonal arrangedcoupling coils 62. In theinputs of the vacuum tube circuits are secondaries 8'2, 55, 66, 12, and 14 of i'nput transformers, while in the output circuits of these tubes'are primaries 10, H, I2, 61, and 68 of output "transformers. operates in exactly the same manner as the translator of thesystem of Fig. 4, that is, the grids biased sufllciently to permit OP- half cycles of the five phase currents above the points of intersection of the phases. 1 This trans- 'lator, however, will have a capacity of five time' channels and i! the generator of Fig. 4 produces .taneous reception.

the same frequencyoi900 cycles per second, there will be 900 impulses v only 1/4500 of'a second in length whilethe rapiduniform oc currence' of each V; will produce eflective simul- In Fig.7 a six time channel combined generator-translator system is illustrated schematically and arranged to represent a mechanical 1/2700 of a second in length..1

This five time channel system.

per second for each-channel,

rises and falls.

. peated transformers connected in I 3 rotating commutator system. Six vacuum tubes I5 to 20, inclusive, are interconnected successive- 1y by variable output impedances 8| to 28 inclusive, and input impedances 81 to 2, respectively. The elements of these .tubes are supplied 5 by individual batteries, as shown, with each tube having .secondaries to Hill, inelusive of input I their respective grid circuits, and primaries IOI to i 06 of output transformers connected in their respective output cir-'- cuits. I This circuit is substantially an impulse generator or oscillator. For instance, the grid of tube 15 'is made positive in any manner such as by, short circuiting the grid battery, momentarily producing in this tube a plate current which 16 This impulse is impressed on the grid of tube 16 through the potential obtained aorpss the coupling impedance 8|. After a amplification in tube It to compensate for any loss in transmission, the impulse is similarly im- 20 pressed on the grid of tube" through coupling impedance. 82. In this manner, the impulse is propagatedthrough each tube in succession, and will'con'tinue to rotate around the circuit aslong as energy is supplied to the vacuum tubes. speed of rotation of this impulse is-determined by the constants of the circuit, but will have a theoretical limit of that of the speed of light. Because of this fact, the impulse .frequency may used in the same manner as the present car-1 rier without a separate carrier source.

Referring to Fig. 9 of the drawings, the shaded portions'of curvesa, b, c, d, e, and I, represent the plate current in each tube. By continuing the curves of the impulses, it will be noted that-an extremely high six phase current frequency is generated by the tubes, although the other portions of the current waves are eliminated by the grid bias on each tube. The shaded portions, however, may be used for transmitting signaling 40 impulses in the same manner as .in the system of Figs. 4 and 5. A signal may .be impressed upon tube 15 through secondary-winding 95 .and retherethrough into primary winding lill of the output transformer during the time when the tube;15 is operative. This signal will again be transmitted through this tube after the impulse has been propagated through' the other tubes in the system and returned to tube 15. This rotating system, therefore, provides an extremely high speed time dividing commutator entirely electrical. The speed may lie-controlled by controlling the coupling impedances M to 86, inclusive, which actually varies the amplitude of the impulses. If the amplitude of ,these impulses is made small, the time unit thereof is correspondingly smaller and a more rapid rotation is effected. 'As each tube controls a time unit or channel, the time units may be varied in length by changing the grid bias on different tubes. An 60 impul'se'may be increased and a time unit lengthened in a tube by changing the bias to a more eflicientoperating point, or decreased and a time unit'shortened by changing thebias in another direction. Changing-circuit constants will also effect the same result. The control impedances BI to it may be connected to a common-control means for uni-control operation.

. In; Fig. 8 a tandem arrangement of a six time channel system is shown with vacuum tubes lit 7 to H5, inclusive, input transformers ill to I22, inclusive; and three winding output transfornn ers I21 to I28, inclusive, respectively. This system is a combined generator-translator system similar to the system of Fig.

The 25 I '1, but has a slightly (5 different principle of operation. There is also included'a synchronlzer I3 I for keeping a receiving commutator in step with a transmitting commutator. In this system a starting switch I32 for placing a positive bias froma battery Ill onto vacuum tube H8 is connected in'the grid circuit of this tube only. Six channels A, B, C,

D, E, and F having inputs and outputs to the system may correspond with the single channels in the preceding explanatory figures. A feature of this-circuit is the delay coupling units I35 to I40 which transfer the impulses from the plate circuits of preceding tubes to the grids of succeeding'tubes at a certain time rate. These units have variable condensers Ill to I48, inclusive, for controlling the time de?ay of theimpulses, all of output transformer. I24 and to the grid of'tube II'I' through delay unit I35. The tuning of this delay circuit. determines the time of operation of the tube III which in turn transmits the impulse to tube III. 'The last tube 5, through circuit I40 transmits the impulse back to tube III for obtaining the continuous rotating action. After the first depression of key I32, the grids are all biased by the common battery I02. The operation of this system is practically the same as that of Fig. 7, and maibe represented by Fig. 9, except that the generated waves may have differently shaped peaks.

' The system in Fig. 8 may be considered a re-. ceiving commutator with an input I50 which is a single pair, of conductors orthe output of a space radio receiving system. The transmission over the'circuit is impressed upon the input transformers II! to I22,,inclusive, simultaneously. It tube I II ismade operatlveby the rotating impulse which removes the heavy bias, the signal arriving through transformer III will be transmitted through the .tube'to the output of trans-- former I24 which may be connectedwitha re- 1 ceiving device in accordance with-the type of signal being transmitted. 'Iransmissionwill not ocour through any of the othertubes of the heavy normal bias. when the impulse actuatestube m, the signal of channel aor n signal willbetrsnsmittedtooutputtransformer m and to its reproducing device. In this manner each be distributed. to its proper receiving tubes supplied from the common filamentbattery "I", and the sum supplied from a common high potential mm, "I and thegrids grom thecommongrldbiasing potential I", The grid .bissingpotential Itlis connecwd between the grids and filaments through the resistance In of the synchronize: shunted by the rectifier circuits just described. This source of potential is constant and remaining constant, provides a certain speed of rotation to the impulse'through the tubes. When the impulse from the input III is impressed ontransformer-Il hit'is rectified by the rectifier Ill and provides a bias ino'ne par tem by the use of hybrid coils for segregating the 'ticular direction, for instance, decreasing the bias on the tubes. In this way' a slowing up of the 'speedof propagation of the impulse around the circuit is obtained. To neutralize this effect, an equal impulse is impressed on the resistance III through the transformer Ill which is obtained from the third windings of the outputtransformera-I24 to l", inclusive. The increased potential derived from transformer I5I will be neutralized by the potential obtained from transformer I if, and when the output impulses are inexact time relationship with those being received at I5]. Any variation of the impulses being received at IS! with respect to the impulses being-generated in the tubes, will be evidenced by a; bias in one direction or the other in the synchronize'r Ill.

' That is, if the system of Fig. 8 is rotating too rapidly, there will be a differential bias produced in the synchronizer to decrease the speed-at which the impulse is transmitted fromitube to tube. This is caused by the phase differential of impulses arriving at the two transformers IiI and IE4 providing a directional-- bias, dependingupon the time or arriva". If the system in Fig. 8 is completely out of step, it may be started and stopped by thekey I32, to obtain original synchronism, after which the synchronizer Ill will maintain the commutators in synchronism.

' In Fig. 10a modification of the coupling between tubes of a rotating electrical commutator so is-shown. The two tubes I15 and I18 maybe two of a series such as illustrated in Figs. 7 and 8, with their respective input circuits I'll and I", and output circuits Ill and Ill. The feature involved in this circuit isthat the circulating g5 impulse is fed back from an operating tube in a 180 degree phase relationship through transformers Ill and I83. The returning impulse is delayed in itsblockingactiou on.the grids by tuned circuits I'lland I08, to obtain any desired 40 speed or. commutation. I This feed back prevents any tendency of a tube to oscillateyand eliminates the need of a heavy grid bias. Each tube transmits its impulse and then automatically blocks itself until further actuated byv a positive The systems above described have .been' shown transmitting signals in one direction,but twoway communication is obvious over the same sysinput and output'circuits of any one ofthe tubes ofthe thermionic commutators. That is, the same tube may serve ass repeaterin each direction, and any time channel may serve as a twoway signaling channel in the same manner as any telephoneline. .n. Although this invention been disclosed in its preferred embodiments, it is obvious that there are many modifications which may be accom-- plished within the scope of the appended claims. on

whatisclaimedisz- I v 1.. In a multiplex communication system, a transmitting station, a receiving station. a plurality ofsignsl sources at said transmitting-station, a corresponding plurality of receiving dev I vices atesid receiving station, a thermionic commutator st eachof said stations comprising a plurality of thermionic devicesarranged in tan.- dem, ssiddevices being made operative. in a serial order at mutually exclusive for impressing on of said evices' from one of saidsignal sources, and means at said receiver for connecting one of said receivingdevices to each of' said electronic devices at said receiver, said thermionic commutator at u tervals, means 7 saidreceiver distributing. the signals from said signal sources to respective receiving devices.

2. A thermionic commutator comprising a plurality of interconnected thermionic devices arranged in tandem, means for transmitting a current impulse through each of said devices in series, and means for blocking each of said devices immediately after transmission of said impulse therethrough.

3. A thermionic commutator in accordance with claim 2, in which-said last mentioned means includes a feedback transformer for each of said devices.

4. A thermionic commutator comprising a plurality of thermionic devices connected in cyclic order, means for directly connecting the output of the preceding device with the input of the succeeding device, said means including inductive and capacitive elements for delaying the transmission of an impulse therebetween a definite said delay circuits varying thetransmission of impulses through said devices.

6. In a multiplex transmission system, rality of thermionic devicesdocated at one station, a duplicate plurality of thermionic devices located at a second station, delay circuits intermediate each of said devices at each of said stations for delaying the transmission of an impulse therebetween; means for biasing said thermionic devices at said second station, the adjustment of said biasing means and said delay circuits delaying the transmission of said-impulses through said devices, means for varying a pluthe bias on said devices by the impulses gen-' erated at said second station, and means for varying thebias of said devices by the impulsesgenerated at said first station the impulses generated at saidsecond station neutralizing the 5 impulses generated at said first station and producing no change in bias on the devices at said second station when the generation of impulses at said first station isin synchronism with the generation of impulses at said second station. 10

7. In an electrical communication system, two stations, a plurality of signaling sources at said two stations, a corresponding plurality of electronic devices arranged in cyclic order located at each of said stations, said devices being operative 15 at mutually exclusive intervals,'delay circuits at. each station for directly connecting the output of the preceding device with the input of the succeeding device, respectively, and means for transmitting any one signal through any one of 20 said vacuum tubes at each of said stations.

.8. Inan electrical communication system, two stations, corresponding pluralities of individual electronic devices connected in cyclic order located at each of said stations, means for operat- 25 ing said devices in serial order in synchronism at discrete intervals, delay circuits at each station for directly connecting the output of the preceding device with the input of the succeeding device,

respectively, a plurality of signal sources, and

means for transmitting the signals from said sources over a pair of said devices in a definite order. g

9. In a multiplex communication system, a pinrality of thermionic devices mutually connected '5 in cyclic order, means for initiating arotating electrical impulse in one of said devices, delay circuits directly connected to the output of the preceding device and the input of the succeeding device for circulating said impulses through said 0 devices at a super-audible frequency at mutually exclusive intervals, and means for transmitting a plurality of signals on said frequency.

ALEXANDER MoLEAN NICOLSON. 

